The present invention relates to an image forming apparatus that forms a color image by overlapping a plurality of images. More specifically, the present invention relates to an image forming apparatus that forms a mark for image adjustment on a transportation belt disposed while coming into contact with a photosensitive unit used for forming an image.
In the past, in an image forming apparatus having a color printing function, a color image is formed in such a manner that images of colors of cyan (C), magenta (M), yellow (Y), and black (K) are formed and overlapped with each other. Likewise, since the plurality of images needs to be overlapped with each other, an electrophotographic type image forming apparatus performs an image adjustment so that a difference does not occur in the positions or concentrations of the images. As for the image adjustment, for example, a resist pattern as a mark for image adjustment is formed for each color, an offset amount (adjustment value) between the resist patterns of a reference color and an adjustment color is obtained, and then the positional offset of the image is corrected on the basis of the adjustment value.
Further, in the image forming apparatus that forms the mark on a transportation belt, when there is a disturbance area such as rubbing traces on the transportation belt, detection precision of the image pattern is degraded due to the damaged portion, and hence correction precision is degraded. As a technology designed to solve this problem, for example, a related image forming apparatus detects an area without disturbances on a transportation belt, and forms a resist pattern on the area without disturbances.